The currently available high-power conversion is implemented by using shunt power switches. In the conventional high power full bridge converter in FIG. 1, the first bridge leg is composed of power switches Q1, Q2, Q3 and Q4, the second bridge leg is composed of power switches Q5, Q6, Q7 and Q8. Such a circuit configuration is similar to the conventional full bridge converter that the parallel bridge legs need no additional control, resulting in a reduced conduction current for each power switches. However, as the output power increases, the number of parallel power switches increases as well. Moreover, since the power switches may not be identical in every parameter and synchronous driving for the gates of the parallel power switches is hard to implement, the current from each parallel power switches may not be identical.
Moreover, in order to reduce the switching loss and the switching stress of the power devices, phase-shift modulation is generally used. FIG. 2 shows the waveforms of the conduction current of the power switches in FIG. 1. It is found that, due to the parallel configuration, the effective conduction current for the power switches in each bridge leg is similar.
Moreover, two full bridge phase-shift modules can be used as shown in FIG. 3. The phase delay between the two full bridge phase-shift modules helps to improve the current ripples and overcome the problems due to difficulty in heat dissipations in the single phase-shift module configuration. Also, like the converter in FIG. 2, the increased number of bridge legs leads to higher cost. Similarly, the converter having three full bridge modules is as shown in FIG. 4, resulting in problems as the converter in FIG. 3.